1. Field of the Invention
The invention resides in the field of electrodialysis cells and more particularly relates to electrode reversal systems for preventing the accumulation of scale within the cathode chamber.
2. Description of the Prior Art
In electrodialysis cells the problem of scale buildup due to the formation of insoluble salts within the cathode chamber is well known. An accumulation of such scale results in electric and hydraulic resistance which reduces the efficiency of the cell and may result in total shutdown if not alleviated. Various techniques have been adopted to prevent, reduce, and/or remove the scale including softening the cathode chamber feed solution or catholyte, adding acid to the catholyte and at periodic time intervals reversing the polarity of the cell to generate acid within the cathode chamber which cathode chamber, upon reversal, functions as an acid generating anode chamber.
The concept of reversal has been refined by such techniques as reducing the flow of anolyte through the anode chamber to produce a high concentration of acid within the chamber to dissolve scale more effectively upon reversal. Such a procedure is disclosed in U.S. Pat. No. 3,341,441, Giuffrida et al., which patent is incoporated herein by reference.
An additional reversal approach constitutes collecting the anolyte in a holding tank and passing the accumulated acid solution through the cathode chamber upon reversal as revealed in U.S. Pat. No. 3,165,460, Zang et al.
The method and apparatus described in detail below presents an improvement in the concept of polarity reversal for the prevention of scale buildup over the techniques of the prior art.